Production of jet fuels



United States Patent O 3,030,299 PRGDUCTION OF JET FUELS Donald P. Plummer, West Norwood, England, assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 19, 1959, Ser. No. 847,088 Claims priority, application Great Britain Mar. 18, 1959 4 Claims. (Cl. 208-96) This invention relates to processes for producing aviation fuels, particularly aviation jet fuels, and to liquid hydrocarbon mixtures suitable as aviation fuels.

In recent times it has become generally recognized that one of thefniain requirements for suitable aviation fuels is that they should have a high calorific value calculated on a weight basis. This requirement is particularly important forfuels used by long range aircraft that require a high payload, for the greater the energy output of the fuel per unit weight, the less fuel the aircraft need carry for a given range, thus providing the opportunity for a greater payload. This is very important to commercial airline operators but is no less important to long range military aircraft which, by virtue of modifications in design, particularly in the tendency toward thinner wing sections as required by high speed, high altitude flight, have less space for fuel storage and consequently require the highest available energy output from the limited fuel they can carry. However, not only is it desirable for aviation fuels, particularly jet fuels, to have a high calorific value, it is at the same time necessary for satisfactory fuels to satisfy other requirements, e.g., for volatility, freezing point and thermal stability. Economic considerations are also of the utmost importance and cheapness and convenience of production, e.g., using existing refinery equipment, are factors to be desired.

It has now been found that a petroleum fraction may be produced using existing refinery streams which has highly desirable properties that make it satisfactory for use as an aviation jet fuel component. This fraction has a high net calorific value per unit weight, i.e., in excess of 19,000 b'.t.u./lb., it has a suitable boiling range and freezing point and by virtue of a very high parafiinic content also possesses maximum thermal stability. By blending this fraction with other hydrocarbon components it is possible to produce jet fuels of suitable volatility, and which meet the specifications laid down for jet fuels, e.g., as laid down for jet fuels of the JP-4 type.

Accordingly, the present invention comprises a process for the production of aviation fuels, comprising catalytically reforming a petroleum fraction having an initial boiling point above 60 C. and a final boiling point not above 150 C. using a platinum containing catalyst, separating by fractional distillation from the resulting reformate a heavy fraction having an initial boiling point not below 80 C., extracting the said fraction with a solvent selective for aromatics to obtain a raffinate substantially free from aromatics and blending said rafiinate with a minor proportion of a butane or pentane in an amount adequate to impart the desired volatility to the blend. Herein, the boiling ranges and initial end boiling points are based on an ASTM distillation.

The butane or pentane which is blended with the raffinate may be any one or a mixture of normal or isobutane, normal-, isoor nee-pentane. A preferred blending component is n-pentane. The butanes may be added to the raflinate in the proportion of up to 6% by weight, and preferably in the proportion up to 3% by weight. The pentanes may be added to the raflinate in the proportion of up to 30% by weight, and preferably in the proportion up to 15% by weight. The addition of up to 10% by weight of n-pentane is very suitable in carrying out the process according to the present invention.

ICC

The petroleum fraction which is subjected to the catalytic reforming treatment may be derived from petroleum by any means. For example, it may be a straight run naphtha or a catalytically or thermally reformed naphtha or catalytically cracked naphtha or a mixture of any one of these. Preferably, the feed stock is a straight run naphtha. The feed stock should preferably have an initial boiling point not below C. and a final boiling point not above 145 C., more preferably not above 140 C. Generally there will be used a feed stock having an initial boiling point of about 80 C. and a final boiling point of about 135 C.

The catalytic reforming treatment (e.g., platforming) is preferably carried out in the presence of an acidic plati num catalyst in the presence of hydrogen under pressure. Reforming is effected with a catalyst consisting of platinum on an acidic support, the platinum, which is the primary active component, constituting 0.1% to about 2.0% by weight of the catalyst. The platinum may be applied to the acidic support in any one of a number of ways, such as by impregnation with colloidal platinum or colloidal platinum sulfide, by impregnation with solutions of soluble platinum salts, e.g., chloroplatinic acid or tetramine platinous nitrate, or by ion exchange with platinum salts. The acidic support for the platinum may be, for example, a synthetic silica-alumina composite, or it may be a non-acidic carrier which is made acidic by the addition of such substances as boric oxide, phosphoric acid or halogen. Thus, for example, adsorptive alumina containing a small amount of fluorine and/or chlorine, e.g., 0.1 to 2% by weight, is a suitable support for the platinum.

The catalyst is used in the form of a fixed foraminous bed which may be fluidized but is preferably static and the liquid hydrocarbon to be treated is passed through the bed of catalyst in the vapor phase.

The reforming treatment, which is endothermic, may be carried out in a reactor or reaction tube with means for applying heat, or a series of separate untreated reaction vessels may be employed with interstage heating of the reactant stream. A combination of these two methods may also be used. The initial stages of the reaction may be advantageously carried out in long narrow reaction tubes filled with catalyst and maintained at a nearly uniform temperature throughout its length by being immersed in a heated fluidized bed of sand or similar inert powdered material.

The reaction temperature is preferably maintained near the maximum consistent with continuous operation without loss of catalyst activity and is preferably above 480 C. Temperatures up to about 570 C. can be employed.

A substantial partial pressure of hydrogen is maintained at all times in the reaction zone, the value may be as low as 100 pounds per square inch but may be as high as 900 pounds per square inch and is maintained at the required value by maintaining a suitable total pressure and by recirculating hydrogen through the reaction zone. Preferably, the water content of'the recirculating gases is controlled and chlorine or a compound yielding chlo rine under the reaction conditions, such as ethylene dichloride or tertiary butyl dichloride, is preferably added either to the feed to the platformer or injected into the stream from one platformer reactor to another.

The reformate is cooled to condense it and preferably directed to a stabilizing column where the lighter hydrocarbons, such as those lighter than butane or pentane, are removed. The stabilized reformate is then passed to a distillation zone where it is subjected to fractional distillation to separate a heavy fraction having an initial boiling point not below 80 C. Preferably, the initial boiling point of the heavy fraction is between C. and 100 C. and more preferably is between C. to Cl De- 'pylene glycol and 8% by weight of water.

pending on the final boiling point of the initial feed stock I used the heavy reformate fraction may have a final boiling point of from about 120 C. to 160 C. It is preferred that this heavy reformate is further fractionated to remove the material boiling above 135 C. and more preferably to remove the material boiling above 120 C.

The solvent that may be used for treating the reformate may be any one of those that selectively extract the aromatic hydrocarbons from a hydrocarbon mixture, e.g., sulfur dioxide, nitrobenzene and the extraction may be carried out by means of vapor-liquid or liquid-liquid extraction, for example, according to the Clorex, or Edeleanu methods. Glycolic solvents may also be used to eX- tract the aromatics from the platformate. Examples of suitable glycolic solvents are diethylene glycol, ethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and these may be used alone or as mixtures with one another. Sulfolane and its various derivatives may be employed as the solvent. Water may also be present in the solvent media. The preferred solvent media is a mixture of diethylene and dipropylene glycol containing from 0.5 to 10% by weight of water. The presence of the water increases the selectivity of the solvent and prevents loss of solvent to the rafiinate. The ratio of solvent to platformate by volume in the extraction system may vary between 5:1 and 20:1 but preferably is within the range 7:1 to 14:1.

The extraction system maybe a countercurrent multistage extraction system, e.g., a column containing packing material or sieve plates, a rotating disc contactor, a multiplicity of mixer settler combinations and the number of theoretical stages should be at least 5. The reformate feed is introduced into the extraction system in which the temperature is maintained at between 125 C. and 155 C. and under a pressure sufiicient to maintain liquid phase operation. The rafiinate is led from the top of the extraction system to a stripper column in which the solvent is removed from the rafiinate which is then washed with water to give a hydrocarbon product of high parafiinic content containing less than 5% by Weight of aromatics.

The rafiinate obtained as a result of the solvent extraction process by virtue of its very high paraflinic content is thermally stable and has a net calorific value in excess of 19,000 B.t.u./lb. This raflinate when blended with a minor proportion of one or more butanes or pentanes, produces a composition which is suitable for use as an aviation fuel, particularly a jet fuel corresponding to a LIP-4 type.

The invention is illustrated by the following examples.

Example I A straight run naphtha having an initial boiling point of 80 C. and a final boiling point of 135 C. is fed into 'a reactor which contains a catalyst comprising 0.75% by weight of platinum on an alumina carrier having acidic properties which resulted from the initial presence of chlorine on the catalyst. In order to maintain the desired acidic properties of the catalyst, ethylene dichloride is injected with the feed to the reactor. The feed is fed at a rate of 2.6 tons of feed per ton of catalyst per hour. The hydrogen to naphtha molar ratio is 5 to 1 and the catalyst inlet temperature is 505 C. The product leaving the reactor is fractionated to give 87% by weight of debutanized liquid and this is further fractionated to give 72.5% by weight of a heavy reformate with an initial boiling point of 95 C. This heavy reformate contains no naphthenes, the naphthenes in the feed stock having been entirely converted to aromatics, and consists of 65% by weight aromatics and 35% by weight of parafiins. This reformate fraction is extracted with a solvent comprising 56% by weight diethylene glycol, 36% by weight dipro- The extraction is carried out at a temperature of 140 C. and a pressure of from 80 to 90 p.s.i.g. with a solvent ratio of Initial boiling .point, C 50% evap., C 102 Final boiling point, C 144 Net calorific value, B.t.u./lb 19,245 Reid vapor pressure, lbs 0.3

92.5 parts by weight of this raffinate is blended with 7.5 parts by weight of n-pentane to produce a jet-fuel which had the following properties:

Initial boiling point, C 50 Final boiling point, C 140 Freezing point, C --60 Reid vapor pressure, lbs 1.5

Net calorific value, B.t.u./lb 19,300

Example II A rafi'inate is produced by the process described in Example 1 except that before the extraction with the selective solvent, the heavy reformate is further fractionated to remove material boiling above 120 C. This raffinate had the following properties:

Initial boiling point, C 95 50% evap., C Finalboiling point, C Net calorific value, B.t.u/lbQ. 19,360 Reid vapor pressure, lbs 0.3

This rafiinate is blended with n-pentane in the proportion of 90 parts by weight of raffinate to .10 parts by weight of n-pentane to produce a jet fuel having the following properties:

Initial boiling point, C 46 Final boiling point, C 120 Freezing point, C 60 'Reid vapor pressure, lbs 2.1 Net calorific value, B.t.u./lb 19,360

I claim as my invention:

1. A process for the production of thermal-stable aviation jet fuel of high calorific value comprising (1) catalytically reforming a petroleum fraction having an initial boiling .point between about 60 C. and about 150 C. in the presence of an acidic platinum catalyst and hydrogen under pressure to obtain a reformate, (2) separating from said reformate a heavy fraction having an initial boiling point above about 80 C. by fractional distillation, (3) extracting said heavy fraction with an aromatic selective solvent selected from the group consisting of glycolic and sulfolane solvents to obtain high paraflinic content hydrocarbon products containing less than about 5% by Weight aromatics, and

(4) blending the high paraifinic content hydrocarbon with a minor portion of a light hydrocarbon selected from the group consisting of butane, pentane and mixtures thereof.

2. A process in accordance with claim 1 wherein the light hydrocarbon employed for blending is butane and it is added in the proportion of up to 6% by weight.

3. A process in accordance with claim 1 where the light hydrocarbon employed for blending is pentane and it is added in the proportion of up to 30% by weight.

4. A process in accordance with claim 1 wherein the petroleum fraction has an initial boiling point not below 80 C. and a final boiling point not above C.

Ruedisulj Feb. 17, 1959 Findlay Aug. 11, 1959 

1. A PROCESS FOR THE PRODUCTION OF THERMAL-STABLE AVIATION JET FUEL CALORIFIC VALUE COMPRISING (1) CATALYTICALLY REFORMING A PETROLEUM FRACTION HAVING AN INITIAL BOILING POINT BETWEEN ABOUT 60*C. AND ABOUT 150*C. IN THE PRESENCE OF AN ACIDIC PLATINUM CATALYST AND HYDROGEN UNDER PRESSURE TO OBTAIN A REFORMATE, (2) SEPARATING FROM SAID REFORMATE A HEAVY FRACTION HAVING AN INITITAL BOILING POINT ABOVE ABOUT 80*C. BY FRACTIONAL DISTILLATION, (3) EXTRACTING SAID HEAVY FRACTION WITH AN AROMATIC SELECTIVE SOLVENT SELECTED FROM THE GROUP CONSISTING OF GLYCOLIC AND SULFOLANE SOLVENTS TO OBTAIN HIGH PARAFFINIC CONTENT HYDROCARBON PRODUCTS CONTAINING LESS THAN ABOUT 5% BY WEIGHT AROMATICS, AND (4) BLENDING THE HIGH PARAFFINIC CONTENT HYDROCARBON WITH A MINOR PORTION OF A LIGHT HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF BUTANE, PENTANE AND MIXTURES THEREOF. 